/*
 * Copyright [2013-2021], Alibaba Group Holding Limited
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

/*
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.alibaba.polardbx.executor.mpp.util;

import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.ImmutableMultiset;
import com.google.common.collect.ImmutableSet;

import java.util.function.Function;
import java.util.stream.Collector;

public final class ImmutableCollectors {
    private ImmutableCollectors() {
    }

    public static <T> Collector<T, ?, ImmutableList<T>> toImmutableList() {
        return Collector.<T, ImmutableList.Builder<T>, ImmutableList<T>>of(
            ImmutableList.Builder::new,
            ImmutableList.Builder::add,
            (left, right) -> {
                left.addAll(right.build());
                return left;
            },
            ImmutableList.Builder::build);
    }

    public static <T> Collector<T, ?, ImmutableSet<T>> toImmutableSet() {
        return Collector.<T, ImmutableSet.Builder<T>, ImmutableSet<T>>of(
            ImmutableSet.Builder::new,
            ImmutableSet.Builder::add,
            (left, right) -> {
                left.addAll(right.build());
                return left;
            },
            ImmutableSet.Builder::build,
            Collector.Characteristics.UNORDERED);
    }

    public static <T> Collector<T, ?, ImmutableMultiset<T>> toImmutableMultiset() {
        return Collector.<T, ImmutableMultiset.Builder<T>, ImmutableMultiset<T>>of(
            ImmutableMultiset.Builder::new,
            ImmutableMultiset.Builder::add,
            (left, right) -> {
                left.addAll(right.build());
                return left;
            },
            ImmutableMultiset.Builder::build,
            Collector.Characteristics.UNORDERED);
    }

    public static <K, V> Collector<V, ?, ImmutableMap<K, V>> toImmutableMap(Function<V, K> keyMapper) {
        return Collector.<V, ImmutableMap.Builder<K, V>, ImmutableMap<K, V>>of(
            ImmutableMap.Builder::new,
            (builder, value) -> builder.put(keyMapper.apply(value), value),
            (left, right) -> {
                left.putAll(right.build());
                return left;
            },
            ImmutableMap.Builder::build);
    }

    public static <K, V, O> Collector<O, ?, ImmutableMap<K, V>> toImmutableMap(Function<O, K> keyMapper,
                                                                               Function<O, V> valueMapper) {
        return Collector.<O, ImmutableMap.Builder<K, V>, ImmutableMap<K, V>>of(
            ImmutableMap.Builder::new,
            (builder, object) -> builder.put(keyMapper.apply(object), valueMapper.apply(object)),
            (left, right) -> {
                left.putAll(right.build());
                return left;
            },
            ImmutableMap.Builder::build);
    }
}
